Device for controlling flow rate of a direct injection fuel pump

ABSTRACT

The invention concerns a method for controlling high pressure fuel supply of a set of injectors connected to a common high pressure chamber, called common rail C in a direct injection fuel circuit, through a high pressure pump (P), by acting on the low pressure supply of said pump (P) through an electromagnetic slide valve (E), controlled by the computer managing the operating conditions of the engine which consists in providing, inside the electromagnetic valve (E) one or more internal leakage flows, either from high pressure to low pressure, or from low pressure upstream of the electromagnetic valve (E) to the low pressure downstream thereby solving the specific problems related to the three operating modes of the engine: engine brake, engine shutdown, idle speed.

The present invention relates to a device for controlling the flow rateof a direct injection fuel pump.

The injection system, known as DFI (Direct Fuel Injection), comprises ahigh pressure pump which supplies fuel under high pressure to a commonchamber, conventionally designated by the expression “common rail”, towhich the injectors are directly connected.

Various means have been proposed to obtain a control of the flow rate ofthe fuel, whether gasoline or gas-oil for motors supplied by injectors:either one controls the flow rate of the pump which supplies theinjectors with high pressure fuel, or one acts downstream of the pump onthe high pressure circuit by recycling the excess fuel; or else one actsupstream of the pump on the admission circuit of the fuel to the pump,to let only the desired quantity of this fuel arrive at the highpressure pump.

Generally speaking, in the known supply systems for injectors for dieselengines, the high pressure pump supplies the common chamber feeding theinjectors, an excess of fuel, the unconsumed fuel being then returned tothe reservoir.

Devices of this type are described in the French patents 2 744 765; 2767 932; 2 769 954 and in EP 0 974 008.

These devices have three drawbacks:

-   -   there is a loss of energy because the pump supplies at high        pressure an excess quantity of the fuel;    -   the return of the unconsumed fuel at high temperature presents a        supplemental risk;    -   the cost of production is higher.

The present invention relates to a device for the control of the flowrate as fuel admission into the high pressure pump in a DFI system bymeans of which the high pressure pump will deliver to the commonchamber, or to the “common rail”, only very precisely the volume of fuelnecessary for the operation of the motor.

But from the time at which the high pressure pump produces only the veryprecisely necessary quantity, it poses problems for the three followingcases of operation: operation during engine braking, which is to saywhen there should be no fuel arriving at the injectors whilst the highpressure pump is still mechanically driven; stopping the motor, becauseit is then necessary to evacuate the high pressure fuel that is in thecommon chamber; and idling, for which a very high precision of the flowrate supplied is necessary.

The process according to the present invention consists in providing,within the electrovalve controlling the arrival of low pressure fuel tothe inlet of the high pressure pump, one or several internal leakagepaths either from the low pressure upstream of the electrovalve towardthe downstream low pressure, or from the high pressure toward the lowpressure, which permits regulating the particular problems which arisefor the three following modes of operation: motor braking, motorstopping and idling.

By way of non-limiting example, and to facilitate comprehension of theinvention, there has been shown in the accompanying drawings:

FIG. 1 a schematic view of a DFI supply circuit.

FIG. 2 a view of a pump supplying high pressure fuel provided by acontrol device according to the invention.

FIG. 3 a view of a second modified embodiment.

FIG. 4 a view of a third modified embodiment.

FIG. 5 a fragmentary view of FIG. 4, on an enlarged scale, showing afourth modification.

FIG. 6 a diagram showing the operation of the installation.

FIG. 7 a diagram showing the operation with an additional leakage path.

FIG. 8 an example of the practice of the invention.

In all these figures, the same elements have the same referencenumerals.

Referring to FIG. 1, it will be seen that the high pressure fuel supplycircuit comprises a fuel reservoir R; a low pressure pump or forcefeeding pump B; an electrovalve E for flow rate control, locatedupstream of a high pressure pump P; a pressure relief valve D; a highpressure chamber C (usually called a common rail) to which are connectedthe injectors I.

The pump P can be any type of pump capable of providing the chamber Cwith gasoline under pressure.

In the example described above (which is not limiting) this pump P is apump of the so-called transfer pump type, which comprises an oil portionand a gasoline portion which are separated from each other in a sealedmanner. The oil, subjected by the pump to an alternative oscillatingmovement, acts on a deformable element which exerts a pumping action onthe gasoline.

The transfer pump is shown schematically in FIGS. 2, 3 and 4 and is notshown in detail because it is well known and is not the subject of thepresent invention.

The brief description which follows has for its object to facilitate thecomprehension of FIGS. 2 to 4.

The oil is subject to alternating back and forth movements by hollowpistons 1. These pistons are given an alternating movement because theybear by their head 2 on an oscillating plate. This oscillating plate isnot shown because it is a known means. When a piston 1 moves (upwardlyin FIG. 2) in its cylinder 4, the oil raises the flap valve 5. Adeformable member 9, in the form of a bellows, is fixed in a sealedmanner at one end 6 to the support of the cylinder 4 and at its otherend 8 to the flap valve 5. When the piston 1 moves in the reversedirection, the flap valve 5 lowers. As a result, the back and forthmovements of the oil give a back and forth movement to said flap valve 5and hence cause elongations and contractions of the bellows 9.

The bellows 9 is disposed in a chamber full of gasoline. This chamber isnot shown because such an arrangement is known. The extensions andcontractions of the bellows 9 cause a pumping effect.

Each chamber in which a bellows 9 is disposed comprises a conduit 10which communicates on the one hand with the low pressure circuit 20through a non-return flap valve 21 and on the other hand with the highpressure circuit 32 through a non-return flap valve 31.

When the bellows 9 is extended under the force of high pressure of theoil, it presses the gasoline at the same pressure through the flap valve31; when it retracts, the gasoline supplied by the pump B passes throughthe non-return valve 21 and enters the chamber in which the bellows 9 isdisposed.

There is utilized an upstream regulation of the flow rate of gasoline,by regulating the flow rate of gasoline arriving at the pump P by meansof an electrovalve 40 disposed in the inlet channel 23 of the lowpressure pump B and distributing the gasoline to the supply circuit 20of said pump P by a conduit 22 a.

It is known to persons skilled in the art that, in practice, it is verydifficult to produce an electrovalve with a slide having no internalleakage, which is a drawback.

The present invention consists in using this drawback by using internalleakages of the electrovalve 20 to solve the problems set forth above.

To do that, according to a first embodiment, there is attached to theconduit 32, which collects the high pressure from the pump P, a branch32 a leading to the electrovalve 40 for regulation of the low pressureflow rate going to the pump, so as continuously to recycle a leakageflow of gasoline under high pressure toward the low pressure circuitthrough said electrovalve 40.

As can be seen in FIG. 2, the high pressure gasoline from the non-returnflap valve 31 is collected by the channel 32, which supplies the chamberC (or common rail). This channel 32 comprises a first branch 32 a whichleads to the electrovalve 40, and a second branch which leads to anoverpressure flap valve D.

The electrovalve 40 is constituted by a body 41 in which is disposed ajacket 42 in which slides a slide 43 which is subject on the one hand toa spring 44 and on the other hand to an electromagnet or motor 45. Theslide 43 comprises two peripheral throats 47 and 46 which are disposedone facing the inlet 32 a of the high pressure collector 32, the otherto the outlet 22 a of the low pressure toward the low pressure collector22.

In normal operation, the throat 46 is uncovered such that the lowpressure gasoline arriving by channel 25 communicates with channel 22 athrough the passage provided between the upper end of the jacket 42 andof the throat 46. The size of this passage varies as a function of theposition of the slide 43 and it is thus that the flow rate of lowpressure gasoline arriving at the pump is regulated as a function of theneeds of the motor.

When the electrovalve 45 is not excited, the spring 44 repels the slide43 and the throat 46 penetrates the jacket 42; the only low pressuregasoline flow rate which arrives at the channel 22 a is a leakage flowrate, at low pressure, which is the result of the functional playnecessary between the jacket 42 and the slide 43.

There is similarly provided a leakage flow rate, but at high pressure,from the throat 47 toward the chamber 49 which is located at the lowerend of the body 41 of the electrovalve and which communicates with thelow pressure through the central passage 48 which passes through theslide 43.

The internal architecture of the electrovalve 40 is determined such thatthe leakage flow rate of high pressure gasoline toward low pressure (in47 a) will be greater than the leakage flow rate of the low pressuregasoline upstream of the electrovalve toward the low pressure downstream(in 46 a).

When the motor operates as a motor brake, the electromagnet 45 is nolonger excited, but the motor turns, and the pump P is thus driven bythe motor to which it is mechanically connected, the supply of lowpressure gasoline toward the channel 22 is cut off; but there is a flowrate of gasoline arriving at said channel 22 which is the leakage flowrate via 46 a of the low pressure upstream to the low pressuredownstream.

When the motor is stopped, there remains gasoline under high pressure(about 200 bars) in the channel 32 and the chamber C. This high pressuregasoline will, little by little, discharge itself by the leakage at 47 atoward the reservoir R.

The respective dimensions of the spaces 46 a and 47 a must be determinedsuch that the leakage flow rate making use of the space 47 a will alwaysbe greater (and at least equal) to the leakage flow rate occupying thespace 46 a.

If there is designated by:

Q=the high pressure flow rate arriving at collector 32

Q1=the low pressure flow rate arriving at collector 22

Q2=the low pressure leakage flow rate in 46 a

Q3=the high pressure leakage flow rate in 47 a

then we have the following equations:

Q=Q1+Q2−Q3 with the following condition: Q2 is negligible

Q=Q1+Q2−Q3 with the following condition: Q3≧Q2 and Q1 is negligible whenit is desired to cancel the flow rate Q.

And when the motor is stopped:

Q=Q1+Q2−Q3 with Q1 and Q2 non-negligible, which is to say, a negativeflow rate and hence a decrease of the pressure in the rail.

FIGS. 3 and 4 show two other modified embodiments using this process.

According to a first modification (FIG. 3) there is added to theelectrovalve with a slide (40-43) a controlled non-return flap valve,which is interposed between the low pressure (LP) upstream and the lowpressure (LP) downstream of the electrovalve.

According to a second modification (FIG. 4) there is added a device forregulation of leakage at the high pressure outlet (HP) of theelectrovalve.

As before, on the conduit 32, which collects the high pressure from thepump, there is disposed a branch 13 a leading to the electrovalve 40 forregulation of the low pressure flow rate from the pump, so as to recyclepermanently through the space 47 a a gasoline leakage flow rate underhigh pressure toward the low pressure circuit through said electrovalve40.

In the case of the modification shown in FIG. 3, there is a non-returnflap valve 50 between the channel LP 23, located upstream of theelectrovalve 40 and the LP channel 22 a, located downstream.

The non-return flap valve 50 is controlled by the electromagnet 45 bymeans of a push rod 51. The flap valve is counter held in closedposition by a spring 52 bearing on a support 53, provided with openings54; this support 53 being in bearing relationship between the slide 43and the electrovalve 40.

In the rest position, the electrovalve 40 is closed. The ball 50 restson its seat in a sealed fashion and the slide 43 covers the supplyopening 42 a. The internal loss of electrovalve 40 is contained in theenvelope 41 of the slide 43. This is the “zero flow rate” position,which is to say the prevention of the flow rate Q1+Q2.

In operation, which is to say when the electrovalve 40 performs itsregulation task, the electromagnet 45 is actuated; the rod 51 raises theball 50 and, by means of the support 53, presses the slide 43, whichuncovers more or less the opening 42 a supplied with LP gasoline. ThisLP gasoline passes through the openings 54 of the support 53 and, theball 50 being raised, arrives at channel 22 a which supplies the LPsupply conduit 22.

The LP gasoline flow rate arriving at the HP pump is thus regulated.

So as to guarantee a substantially constant piloting effort, afunctional set is provided between the ball 50 and the support 53, withthe following equation:(LP×Ball section)+Spring force 52=F return force 44.

Upon motor stopping, the electromagnet 45 is deactivated, the slide 43closes the opening 42 a and the ball 50 returns to its seat.

The high pressure which remains in conduits 32/32 a will diminish,because of the internal leakage, at 47 a, of the electrovalve 40 towardthe channel 23 such that the remaining pressure HP is progressivelydischarged.

This modification has the advantage of ensuring a real zero flow ratewithout leakage of the force feeding pressure (LP) as is the case in theexamples of FIG. 2.

On the other hand, as there is no longer leakage on the LP circuit, itis no longer necessary to have a small leakage on the HP, small leakagewhich has no negative effect on the operation of the high pressure pump.

FIG. 4 shows another modified embodiment, in which the same elementsbear the same reference numerals.

The object of this modification is to provide a so-called “functionbypass” function, which permits, among other things, short circuitingthe HP pump for LP starting.

Under certain starting conditions, the motor starter does not turn fastenough that the HP pump can provide a sufficient flow rate to theinjectors.

It is thus interesting to short circuit, at least partially, the pump Pso as directly to supply the common rail C with LP gasoline to ensure LPstarting.

Referring to this FIG. 4, it will be seen that the return spring 44 ofthe slide 43 is enclosed in a cage of variable length, constituted bytwo elements 60/61 that can move toward each other.

The low pressure gasoline from the force feeding pump B through thechannel 23 arrives laterally into the chamber 64 in which is located thecage 60/61, which encloses the return spring 44.

This chamber 64 comprises at its upper end an opening 62 whichcommunicates through a channel 63 with the rail C and hence the HP whichis located there.

At rest, the pieces are in the position shown at FIG. 4.

The low force feeding pressure arriving through the channel 23 entersthe chamber 64 of the electrovalve 44 and communicates via the opening62 and the channel 63 with the rail C. This ensures the bypass operationset forth above; on the other hand, this also ensures the operation ofdischarging the common rail C in case of stopping.

At the beginning of regulation, the electrovalve 45 pushes back theslide 43 and the cage 60/61 closes the opening 62 and hence thecommunication between the LP inlet and the rail C. If the flow ratesupplied by the HP pump is greater than the flow rate consumed by themotor (valve leakage for example) the pressure in the HP circuit rises,and an HP rail loss toward LP is regulated through the opening 62. Theexcess flow rate is thus recycled to the LP.

In the narrow regulation phase, the electromagnet 45 pushes the slide 43back, which compresses the spring 44 to which the portion 60 of the cage60/61 is applied, against the opening 62, which is thus closed; uponreturning, the slide 43 causes the channel 23 to communicate with thethroat 46 connected to the channel 23 a. The BP gasoline flow ratearriving at the HP pump is thus regulated.

Obviously, it is necessary to avoid inopportune opening of the opening62, and to do this it is necessary to fix the cross-section of theopening 62 such that when the electrovalve 45 applies by means of theslide 43 the portion 60 of the cage against the opening 62, this latterwill be dimensioned such that the maximum pressure of the HP multipliedby said cross-section, will be lower than the load in place of thespring 44.

In FIG. 6 there are shown four curves (I), (II), (III) and (IV), givenby way of example.

The abscissa is graduated as a percentage of PWM (Pulse WidthModulation) which is the usual control means for an electrovalve bymodification of the width of the pulses arriving at the motor 45.

There are two scales on the ordinate, one on the left side, which is ascale of flow rate in cc/min; the other on the right side which is ascale of pressure in bars.

The curve (I) represents consumption of the idling motor: it is thusconstant.

Curve (II) represents the leakage flow rate through the electrovalve: itincreases with PWM (decrease of the drawer/skirt recovery).

Curve (III) represents the increase of flow rate as a function of PWM.

Curve (IV) represents the pressure necessary to open the flap valve60/62 toward the common rail C as a function of PWM.

It will be seen that curve (IV) is not shown from 40% PWM. This meansthat beyond this latter, the force exerted by the spring 44, because ofthe collapse caused by the movement of the slide (upward in FIG. 4)controlled by the motor 45, is such that the flap valve 60/62 cannotopen, the portion 60 of the cage 60/61 remaining applied against theopening 62.

Examination of curves (I) and (II) shows that, at idling, the flow rateof the internal loss of the electrovalve is greater than the consumptionof the motor. As a result, the computer which controls the motor willcontrol the PWM such that the flap valve 60/62 can open and that theexcess of gasoline from the internal leakage will be returned to theupstream LP.

In this case, as the flap valve 60/62 is opened, the HP which is sent tothe common rail C through the channel 32, returns through the channel 63toward the channel 23, through the chamber 64 of the electrovalve 40;because the pressure prevailing in the common rail C and thus in thechannel 63 is greater than that prevailing in the channel 23.

There is thus a reversal of the circulation of the gasoline duringstopping of the motor.

This possibility of reversal of the circulation of the motor can be veryinteresting.

Thus, it permits lowering the high pressure in the common rail C forvery particular operating modes of the motor.

In the systems in service at present, when it is desired to lower thehigh pressure, the mixture is enriched, which increases the consumptionand thus lowers the pressure; but this is wasteful.

Thanks to the device according to the invention, the supply can be cutand have a negative flow rate which returns to the reservoir and causesthe pressure to fall in the common rail C.

This arrangement, although satisfactory, can be improved.

Thus it is noted that it is very difficult to obtain sufficientprecision by such regulation, which uses springs and flap valves: therecan thus result, upon idling, irregularities of supply of the injectorswhich means that the motor will not have a stable operation but“hiccup”.

To eliminate this drawback, there is provided, according to theinvention, an additional permanent leakage flow rate in the valve towardthe common rail C, which is to say in the valve 60/62.

Referring to FIG. 5, it will be seen that the portion 60 of the cage60/61 does not rest directly against the opening 62, but on a seat 65 inwhich there is provided one or several conduits precisely calibrated soas to ensure a permanent calibrated leakage flow through said seat 65.

Referring then to FIG. 7, it will be seen that the curve (I) has beenreplaced by the curve (V) which represents a consumption of the idlingmotor+the leakage flow rate through the calibrated opening for leakagethrough the seat 65.

It will thus be seen that the curve (V) is always below the curve (II),which is to say that the consumption of the idling motor added to thepermanent leakage flow rate is greater than the internal leakage of theelectrovalve.

As a result, there is a deficit of the LP gasoline flow rate arriving atthe pump; hence the common rail C will not be sufficiently supplied;this causes the pressure in the common rail C to lower; this decrease ofpressure will be detected and transmitted to the computer which willincrease the PWM, which is to say cause the slide 43 of the electrovalve40 to move, to increase the LP flow rate by moving toward the foot ofthe curve III.

The adjustment of the flow rate being much more precise than theregulation of the pressure, there is thus obtained an excellent controlof idling.

This result is obtained at the price of a loss of overall output of thepump; but this loss is very low and considered as negligible relative tothe result obtained.

FIG. 8 shows an example of embodiment of the device shown schematicallyin FIGS. 5 and 6.

The electrovalve comprises a slide 100 (corresponding to the slide 43)which is actuated by a motor 101 (corresponding to 45). The upstream LP,from the reservoir thanks to the force feeding pump, arrives through thechannel 102 (corresponding to 23), in a chamber 103 (corresponding to64). The downstream LP, from the internal leakage flow, is collected inthe throat 104 (corresponding to 46) and is directed toward the intakeof the HP pump through the channel 105 (corresponding to 22 a). Theinternal leakage of the upstream LP to the downstream LP takes place inthe zone indicated at 106, between the chamber 103 and the throat 104.The slide is counteracted by a spring 107 (corresponding to the spring44) which is located in the chamber 103.

The spring 107 is disposed between the slide 100 and a pusher 108bearing a ball 109 which will close a small channel 110 which opens intoa channel 111 which communicates with the common rail C. The channels110 and 111 are arranged through a member 112 which is fixed to theskirt 114 (corresponding to 42) in which slides the slide 100.

The piece 112 is fixed at the end of the skirt 114 by providing acalibrated passage 113 permitting a permanent leakage.

The channel 111 and the calibrated leakage 113 open into a chamber 115which, through a channel 116 (corresponding to 63), communicates withthe common rail C.

The ball 109 on its seat of the channel 110 and the calibrated passage113 correspond to the flap valve 60/62 and to the leakage 65 of FIG. 6.

The electrovalve shown in FIG. 8 corresponds exactly to that of FIGS. 4and 5 and its operation is identical.

1. Process for controlling the supply of high pressure (HP) gasoline ofa set of injectors connected to a common high pressure chamber, called a“common rail” (C) in a direct fuel injection circuit, called DFI, by ahigh pressure pump (P), comprising steps of: acting on a low pressure(LP) supply of said pump (P) by means of a slide electrovalve (E),controlled by a computer allowing an internal leakage from an upstreamlow pressure, arriving at the electrovalve (E), toward a downstream lowpressure, toward the pump (P), and providing in said electrovalve (E) ahigh pressure (HP) leakage of the gasoline, located in the common rail(C), toward the upstream low pressure.
 2. Process according to claim 1,wherein the electrovalve (E) comprises a chamber (64) receiving theupstream low pressure, the chamber being connected to the common rail(C) by means serving as a non-return valve of calibrated passage, sothat under certain conditions of operation of the motor, the gasolinelocated at low pressure in the common rail can be returned to the lowpressure upstream inlet.
 3. Device for practicing the process accordingto claim 2, of the type comprising: low pressure gasoline supplied by alow pressure pump (B) acting in a reservoir (R); a high pressure pump(P); a common rail (C) supplied by the high pressure pump; and anelectrovalve (E) regulating the supply of the low pressure gasoline tosaid pump (P), an upstream low pressure inlet connecting the pump (B) tothe electrovalve; a downstream low pressure conduit connecting theelectrovalve to the high pressure pump (P); said electrovalve (E)comprising: a slide (43) slidably disposed in a jacket (42) so as tocause the upstream low pressure inlet (23) to communicate with thedownstream low pressure conduit (22 a) supplying the pump (P) by meansof a throat (46) provided in the slide (43); a chamber (64) into whichthe upstream low pressure inlet opens; an orifice (62) connecting thechamber (64) to the common rail by a channel (63); a deformable cage(60, 61) disposed in the chamber so as to be able to controllable restagainst the seat so as to controllably open or close the orifice,calibrated openings allowing some flow to the channel (63) even when thedeformable cage is positioned to close the orifice; a spring (44)disposed in the deformable cage to apply force to the slide; a motor(45) disposed to move the slide against the spring force; wherein theslide, jacket, and throat are constructed and arranged so that a leakageflow occurs between the upstream low pressure inlet (23) and thedownstream low pressure conduit (22 a) by means of play between theskirt (42) and the slide (43), wherein, as a function of the demand onthe motor, a communication can be established between the reservoir (R)and the common rail (C) by the upstream low pressure inlet (23) andchannel (63) through at least one of the orifice (62) and the calibratedopenings.
 4. Device according to claim 3, further comprising a seat (65)against which rests a movable portion (60) of the deformable cage(60/61); said seat (65) being traversed by at least one of thecalibrated openings so as to ensure through said seat (65) a calibratedpermanent leakage.
 5. Device according to claim 3, in which the slide(43) of the electrovalve (E) is traversed by a passage (48).
 6. Deviceaccording to claim 4, in which in normal operation of the motor, the lowpressure gasoline provided by the low pressure pump (B) passes throughthe electrovalve by passing through the throat (46), which is opened bythe movement of the slide (43) moved by the motor (45) against thespring (44) which applies a portion (60) of the cage against the orifice(62).
 7. Device according to claim 3, in which when the motor isstopped, residual high pressure prevailing in the common rail (C) flowstoward the reservoir (R) through the calibrated openings, the chamber(64) and the upstream low pressure inlet (23).
 8. Device according toclaim 3, in which when the motor acts as a motor brake, the injectorsare closed, but the pump (P) is still driven and pumping the leakageflow from the upstream low pressure to the downstream low pressure, thehigh pressure increases in the common rail and presses back the cage(60) by opening the orifice (62) so as to be returned to the reservoir(R).
 9. Device according to claim 3, in which when the motor turns idly,excess high pressure gasoline provided by the pump (P) is returned tothe reservoir (R) through the channel (63), the orifice (62) and theupstream low pressure inlet (23).